Ion source with single-slot tubular cathode

ABSTRACT

An ion source including a chamber housing defining an ion source chamber and including an extraction plate on a front side thereof, the extraction plate having an extraction aperture formed therein, and a tubular cathode disposed within the ion source chamber and having a slot formed in a front-facing semi-cylindrical portion thereof disposed in a confronting relationship with the extraction aperture, wherein a rear-facing semi-cylindrical portion of the tubular cathode directed away from the extraction aperture is closed.

FIELD OF THE DISCLOSURE

The disclosure relates generally to ion sources, and more particularlyto an ion source having a tubular cathode with a single slot.

BACKGROUND OF THE DISCLOSURE

Ion implantation is a process of introducing dopants or impurities intoa substrate via ion bombardment. In semiconductor manufacturing, thedopants are introduced to alter electrical, optical, or mechanicalproperties. For example, dopants may be introduced into an intrinsicsemiconductor substrate to alter the type and level of conductivity ofthe substrate. In manufacturing an integrated circuit (IC), a precisedoping profile often provides improved IC performance. To achieve aparticular doping profile, one or more dopants may be implanted in theform of ions in various doses and various energy levels.

The beam line components of an ion implanter may include a series ofelectrodes configured to extract ions from a source chamber, a massanalyzer configured with a particular magnetic field where just ionshaving a desired mass-to-charge ratio are allowed to pass through theanalyzer, and a corrector magnet configured to provide a ribbon beamdirected to the platen to implant the ions into a target substrate. Theions lose energy when the ions collide with nuclei and electrons in thesubstrate and come to rest at a desired depth within the substrate basedon the acceleration energy. The depth of implantation into the substrateis a function of ion energy and the mass of the ions generated in thesource chamber. In some approaches, arsenic or phosphorus may be dopedto form n-type regions in a substrate, and boron, gallium, or indium maybe doped to create p-type regions in a substrate.

Various types of ion sources may be employed for ionizing feed gases.Such sources may be selected based on the type of plasma intended aswell as an associated ion beam profile for implantation into a targetsubstrate. One type of ion source is a hot-cathode ion source utilizingan indirectly heated cathode (IHC) to ionize a feed gas in a sourcechamber. IHC ion sources may generate a variety of ion species includingdopant ions (e.g. B⁺, P⁺, As⁺) used for implantation into semiconductorsubstrates to control electronic properties of the semiconductorsubstrates. A persistent challenge with IHC ion sources is theimprovement of molecular ion beam currents, particularly P₂ ⁺ dimer andBF₂ ⁺ beam current.

With respect to these and other considerations the present improvementshave been needed.

SUMMARY

The Summary is provided to introduce a selection of concepts in asimplified form, the concepts further described below in the DetailedDescription. The Summary is not intended to identify key features oressential features of the claimed subject matter, nor is the Summaryintended as an aid in determining the scope of the claimed subjectmatter.

An ion source in accordance with an exemplary embodiment of the presentdisclosure may include a chamber housing defining an ion source chamberand including an extraction plate on a front side thereof, theextraction plate having an extraction aperture formed therein, and atubular cathode disposed within the ion source chamber and having a slotformed in a front-facing semi-cylindrical portion thereof disposed in aconfronting relationship with the extraction aperture, wherein arear-facing semi-cylindrical portion of the tubular cathode directedaway from the extraction aperture is closed.

An ion source in accordance with another exemplary embodiment of thepresent disclosure may include a chamber housing defining an ion sourcechamber and including an extraction plate on a front side thereof, theextraction plate having an extraction aperture formed therein, a tubularcathode disposed within the ion source chamber and having a slot formedin a front-facing semi-cylindrical portion thereof disposed in aconfronting relationship with the extraction aperture, wherein arear-facing semi-cylindrical portion of the tubular cathode directedaway from the extraction aperture is closed. The slot may have anangular size in a range of 10 degrees to 180 degrees relative to acircular cross-section of a main body of the tubular cathode. A radialdistance between an exterior surface of a main body of the tubularcathode and an interior surface of the chamber housing is in a range of1 millimeter to 5 millimeters. A shortest distance between a main bodyof tubular cathode and the extraction aperture is in a range of 2millimeters to 10 millimeters.

An ion source in accordance with another exemplary embodiment of thepresent disclosure may include a chamber housing defining an ion sourcechamber and having an extraction plate on a front side thereof and a gasinlet in a rear side thereof, the extraction plate having an extractionaperture formed therein. The ion source may further include a tubularcathode disposed within the ion source chamber between the extractionplate and the gas inlet, the tubular cathode having a slot formed in afront-facing semi-cylindrical portion thereof, the slot disposed in aconfronting relationship with the extraction aperture, wherein arear-facing semi-cylindrical portion of the tubular cathode is closed.The ion source may further include a thermal break in the chamberhousing adjacent the ion source chamber for mitigating temperaturevariations at an interior surface of the chamber housing.

A method of manufacturing an ion source in accordance with an exemplaryembodiment of the present disclosure may include providing a chamberhousing defining an ion source chamber and including an extraction plateon a front side thereof, the extraction plate having an extractionaperture formed therein, and disposing a tubular cathode within the ionsource chamber, the tubular cathode having a slot formed in afront-facing semi-cylindrical portion thereof, the slot disposed in aconfronting relationship with the extraction aperture, wherein arear-facing semi-cylindrical portion of the tubular cathode directedaway from the extraction aperture is closed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a longitudinal cross-sectional view illustrating an ionsource in accordance with an embodiment of the present disclosure;

FIG. 1B is an axial cross-sectional view of the ion source shown in FIG.1A;

FIG. 2 is an axial cross-sectional view of the ion source shown in FIG.1A during operation;

FIG. 3-5 are axial cross-sectional views of the ion source shown in FIG.1A with alternative tubular cathode configurations;

FIG. 6 is an axial cross-sectional view of the ion source shown in FIG.1A with alternative tubular cathode and chamber housing configurations;

FIG. 7 is a flow diagram illustrating a method of manufacturing a ionsource in accordance with an exemplary embodiment of the presentdisclosure.

The drawings are not necessarily to scale. The drawings are merelyrepresentations, not intended to portray specific parameters of thedisclosure. The drawings are intended to depict example embodiments ofthe disclosure, and thus are not to be considered as limiting in scope.In the drawings, like numbering represents like elements.

Furthermore, certain elements in some of the figures may be omitted, orillustrated not-to-scale, for illustrative clarity. The cross-sectionalviews may be in the form of “slices”, or “near-sighted” cross-sectionalviews, omitting certain background lines otherwise visible in a “true”cross-sectional view, for illustrative clarity. Furthermore, forclarity, some reference numbers may be omitted in certain drawings.

DETAILED DESCRIPTION

An ion source in accordance with the present disclosure will now bedescribed more fully hereinafter with reference to the accompanyingdrawings, where non-limiting embodiments of the ion source are shown.The ion source may be embodied in many different forms and are not to beconstrued as being limited to the embodiments set forth herein. Instead,these embodiments are provided so the disclosure will be thorough andcomplete, and will fully convey the scope of the ion source to thoseskilled in the art.

Provided herein are embodiments of an ion source with improved molecularion beam currents. Specifically, embodiments of an ion source having asingle-slot tubular cathode are provided for facilitating larger beamcurrents of molecular ion species, such as phosphorous dimer, trimer andtetramer and BF₂ ⁺, for a given extraction current, relative to ionsources having conventional cathode arrangements. Thus, the ion sourceof the present disclosure may achieve greater throughput and/orincreased maintenance intervals.

Referring now to FIGS. 1A and 1B, a longitudinal cross-sectional viewand an axial cross-sectional view illustrating an ion source 100 inaccordance with an exemplary embodiment of the present disclosure isshown. For the sake of convenience and clarity, terms such as “front,”“rear,” “lateral,” “longitudinal,” “axial,” and “radial,” may be usedbelow to describe the relative placement and orientation of variouscomponents of the ion source 100, all with respect to the geometry andorientation of the ion source 100 as the ion source 100 appears in FIGS.1A and 1B. Specifically, the term “front” shall refer to a side of theion source 100 nearer the top of the page in FIGS. 1A and 1B, and theterm “rear” shall refer to a side of the ion source 100 nearer thebottom of the page in FIGS. 1A and 1B. Said terminology will include thewords specifically mentioned, derivatives thereof, and words of similarimport.

The ion source 100 may include, among other components, a chamberhousing 102 having a first sidewall 104, a second sidewall 106, and anextraction plate 108 coupled to the first and/or second sidewalls 104,106. The extraction plate 108 may include one or more extraction slitsor apertures 110. The chamber housing 102 may further include a basewall 112 having one or more gas inlets 114 in a rear thereof, oppositethe extraction aperture 110. The present disclosure is not limited inthis regard, and in various alternative embodiments the ion source 100may include one or more gas inlets located in any of the first sidewall104, the second sidewall 106, the extraction plate 108, and/or the basewall 112. Together, the first sidewall 104, the second sidewall 106, theextraction plate 108, and the base wall 112 of the chamber housing 102may define an ion source chamber 116.

In some embodiments, the extraction plate 108 may be made ofelectrically conducting material, such as doped Si, doped SiC, aluminum,graphite, molybdenum, tantalum or tungsten. The present disclosure isnot limited in this regard.

As shown, a single-slot tubular cathode 120 (hereinafter “the tubularcathode 120”) may be disposed within the ion source chamber 116 and mayextend between the first sidewall 104 and the second sidewall 106. Invarious embodiments, the tubular cathode 120 may be electricallyisolated from the first sidewall 104 and the second sidewall 106. Invarious embodiments, the tubular cathode 120 may include a cup 124containing a filament 126, and a tubular (or open cylindrical) main body128 coupled at a first end 130 to the cup 124. More specifically, thecup 124 may include a first end 127 extending through the first sidewall104 and coupled to a cathode holder 105, and a second end 129 extendinginto an interior 131 of the main body 128 and secured in place using anyvariety of means. A second end 132 of the main body 128 may be coupledto a repeller 134. As shown, the repeller 134 may include a repellerhead 135 extending from a shaft 137. More specifically, the shaft 137may extend through the second sidewall 106 and may be coupled to arepeller holder 107 and may be electrically isolated from the secondsidewall 106. As shown, the repeller head 135 may be positioned withinthe interior 131 of the tubular cathode 120 and secured in place using avariety of means. In certain embodiments, the shaft 137 may be held inplace by a clamp 133 on the exterior of the ion source chamber 116. Theshaft 137 may have a smaller cross-sectional area than the repeller head135, wherein the repeller head 135 provides a biased surface to confinethe electrons. The shaft 137 is further intended to provide mechanicalsupport and electrical conductivity to the clamp 133.

The main body 128 of the tubular cathode 120 may include a slot 138formed in a front-facing semi-cylindrical portion of the main body 128nearest the extraction plate 108. The slot 138 may be generally alignedwith the extraction aperture 110 in a confronting relationshiptherewith. As will be described in greater detail below, the feed gassupplied to the ion source chamber 116 via the gas inlet 114 may beionized in the tubular cathode 120. In various embodiments, the feed gasmay be supplied in the form of hydrides and fluorides. For example, theion source 100 may be employed for ion implantation of molecular, dimer,and tetramer species derived from a hydride-containing precursorspecies. Examples of hydride species used as precursors for ionsgenerated by the ion source 100 include PH₃ and AsH₃ among otherspecies. Examples of fluoride species used as precursors for ionsgenerated by the ion source 100 include BF₃ and PF₃ among other species.The embodiments of the present disclosure are not limited in thiscontext. In a specific, non-limiting example, BF₂ ⁺ species ions may begenerated by a BF₃ feed gas.

Referring to FIG. 2, an axial cross-sectional view illustrating the ionsource 100 during use is shown. As depicted, the feed gas may beintroduced into the ion source chamber 116 via the gas inlet 114 and anarc plasma 141 may be generated within the interior 131 of the main body128 of the tubular cathode 120 when a potential difference (voltage) isapplied between the tubular cathode 120 and the chamber housing 102. Theplasma 141 generated within the interior 131 of the main body 128 isexpanded towards the extraction aperture 110 through the slot 138. Insome embodiments, and with reference to FIG. 1A, the first sidewall 104,the second sidewall 106, the extraction plate 108, and the base wall 112of the chamber housing 102 are at a same electrical potential.Furthermore, the cup 124, the tubular cathode 120, the clamp 133, andthe repeller 134 are electrically connected to one another and are at asame electrical potential. The ion source 100 may be coupled to variousconventional components not depicted for clarity, including powersupplies for the tubular cathode 120 and the filament 126.

As shown, the plasma 141 may have two distinct regions: a hot plasmaregion 143 located primarily within the main body 128 and havingrelatively high electron temperatures; and a cold plasma region 145located primarily outside of the main body 128, adjacent the extractionaperture 110, and having relatively low electron temperatures. Since themain body 128 has a single, front-facing slot 138 and does not have anyrear-facing slots or apertures (e.g., no slots or apertures formed in arear semi-cylindrical portion of the main body 128), the feed gasintroduced into the ion source chamber 116 at the rear of the chamberhousing 102 is channeled around the exterior of the main body 128 to thefront portion of the ion source chamber 116 where the feed gas isionized in the cold plasma region 145. Thus, the main body 128 largelyshields the feed gas from exposure to the hot plasma region 143 locatedwithin the main body 128, where the molecules of the feed gas couldotherwise be fragmented by energetic electrons in the hot plasma andthus less likely to form desired ion species (e.g., BF₂ ⁺, P₂ ⁺, P₄ ⁺).The formation of desired molecular beam currents (e.g., BF₂ ⁺, P₂ ⁺ andP₄ ⁺ beam currents) is thus enhanced relative to conventional ionsources wherein feed gases are flowed directly through regions of hotplasma. Additionally, as the feed gas migrates from the gas inlet 114 tothe cold plasma region 145, the molecules of the feed gas may collidewith the exterior surface of the main body 128 and the interior surfacesof the chamber housing 102 as indicated by the arrows 147, 149. Thesecollisions may produce thermal reactions (thermal dissociations) in thegas molecules and may result in the formation of dimers and tetramers.

In various embodiments, the slot 138 may have an angular size in a rangeof 10 degrees to 180 degrees relative to the circular cross-section ofthe main body 128. For example, as shown in FIG. 1B, the slot 138 mayhave an angular size of 90 degrees. In other specific examples, FIGS.3-5 depict tubular cathodes 220, 320, 420 having main bodies 228, 328,428 with slots 238, 338, 438 having angular sizes of 60 degrees, 120degrees, and 180 degrees, respectively. The present disclosure is notlimited in this regard.

Referring to FIG. 6, the configuration of the tubular cathode 120 andthe chamber housing 102 may be varied to tune or optimize molecular ionspecies formation relative to the configuration shown in FIG. 2. Forexample, a radial distance between the exterior surface of the main body128 and the interior surfaces of the chamber housing 102 may be reducedrelative to the configuration shown in FIG. 2 to increase the frequencyof collisions between feed gas molecules and the exterior surface of themain body 128 and the interior surfaces of the chamber housing 102 (asindicated by arrows 151, 153) to further enhance the formation of dimersand tetramers. For example, the radial distance between the exteriorsurface of the main body 128 and the interior surfaces of the chamberhousing 102 may be in a range of 1 millimeter and 5 millimeters. Thepresent disclosure is not limited in this regard. Additionally, thedistance between the main body 128 and the extraction aperture 110 maybe reduced relative to the configuration shown in FIG. 2 to reduce theloss of molecular ion species therebetween. For example, a shortestdistance between the main body 128 and the extraction aperture 110 maybe in a range of 2 millimeters and 10 millimeters. Still further,thermal breaks 154, 156 may be incorporated into the chamber housing 102adjacent the ion source chamber 116 to help maintain consistently hightemperatures at the interior surfaces of the chamber housing 102. Thismay promote thermal dissociation of gas molecules colliding with theinterior surfaces of the chamber housing 102. In various embodiments,the thermal breaks 154, 156 may be voids or other thermally insulatingbarriers formed or disposed in the chamber housing 102 adjacent the ionsource chamber 116.

Referring to FIG. 7, a flow diagram illustrating an exemplary method formanufacturing an ion source in accordance with the present disclosure isshown. The method will now be described in conjunction with theembodiments of the present disclosure shown in FIGS. 1A-6.

At block 1000 of the exemplary method, a chamber housing 102 having afirst sidewall 104, a second sidewall 106, and an extraction plate 108coupled to the first and/or second sidewalls 104, 106 may be provided.The extraction plate 108 may include one or more extraction slits orapertures 110. The chamber housing 102 may further include a base wall112 having one or more gas inlets 114 in a rear thereof, opposite theextraction aperture 110. The present disclosure is not limited in thisregard, and in various alternative embodiments the ion source 100 mayinclude one or more gas inlets located in any of the sidewall 104, thesidewall 106, the extraction plate 108, and/or the base wall 112.Together, the first sidewall 104, the second sidewall 106, theextraction plate 108, and the base wall 112 of the chamber housing 102may define an ion source chamber 116.

In some embodiments, the extraction plate 108 may be made ofelectrically conducting material, such as doped Si, doped SiC, aluminum,graphite, molybdenum, tantalum or tungsten. The present disclosure isnot limited in this regard.

At block 1100 of the exemplary method, a single-slot tubular cathode 120(hereinafter “the tubular cathode 120”) may be disposed within the ionsource chamber 116 and may extend between the first sidewall 104 and thesecond sidewall 106. In various embodiments, the tubular cathode 120 maybe electrically isolated from the first sidewall 104 and the secondsidewall 106. At block 1200 of the method, a first end 130 of a tubular(or open cylindrical) main body 128 of the tubular cathode 120 may becoupled to a cup 124 containing a filament 126. More specifically, afirst end 127 of the cup 124 may be extended through the first sidewall104 and coupled to a cathode holder 105, and a second end 129 of the cup124 may be extended into an interior 131 of the main body 128 andsecured in place using any variety of means. At block 1300 of themethod, a second end 132 of the main body 128 may be coupled to arepeller 134. As shown, the repeller 134 may include a repeller head 135extending from a shaft 137. More specifically, the shaft 137 may beextended through the second sidewall 106 and may be coupled to arepeller holder 107 and may be electrically isolated from the secondsidewall 106. As shown, the repeller head 135 may be positioned withinthe interior 131 of the tubular cathode 120 and secured in place using avariety of means. In certain embodiments, the shaft 137 may be held inplace by a clamp 133 on the exterior of the ion source chamber 116. Theshaft 137 may have a smaller cross-sectional area than the repeller head135, wherein the repeller head 135 provides a biased surface to confinethe electrons. The shaft 137 is further intended to provide mechanicalsupport and electrical conductivity to the clamp 133.

At block 1400 of the exemplary method, the main body 128 of the tubularcathode 120 may be provided with a slot 138 formed in a front-facingsemi-cylindrical portion of the main body 128 nearest the extractionplate 108. The slot 138 may be generally aligned with the extractionaperture 110 in a confronting relationship therewith. In variousembodiments, the slot 138 may have an angular size in a range of 10degrees to 180 degrees relative to the circular cross-section of themain body 128. For example, as shown in FIG. 1B, the slot 138 may havean angular size of 90 degrees. In other specific examples, FIGS. 3-5depict tubular cathodes 220, 320, 420 having main bodies 228, 328, 428with slots 238, 338, 438 having angular sizes of 60 degrees, 120degrees, and 180 degrees, respectively. The present disclosure is notlimited in this regard.

At block 1500 of the exemplary method, the configuration of the tubularcathode 120 and the chamber housing 102 may be varied to tune oroptimize molecular ion species formation relative to the configurationshown in FIG. 2. For example, a radial distance between the exteriorsurface of the main body 128 and the interior surfaces of the chamberhousing 102 may be varied to increase the frequency of collisionsbetween feed gas molecules and the exterior surface of the main body 128and the interior surfaces of the chamber housing 102 (as indicated byarrows 151, 153) to further enhance the formation of dimers andtetramers. For example, the radial distance between the exterior surfaceof the main body 128 and the interior surfaces of the chamber housing102 may be in a range of 1 millimeter and 5 millimeters. The presentdisclosure is not limited in this regard. Additionally, at block 1600 ofthe exemplary method, the distance between the main body 128 and theextraction aperture 110 may be varied to reduce the loss of molecularion species therebetween. For example, a shortest distance between themain body 128 and the extraction aperture 110 may be in a range of 2millimeters and 10 millimeters.

At block 1700 of the exemplary method, the chamber housing 102 may beprovided with thermal breaks 154, 156 adjacent the ion source chamber116 to help maintain consistently high temperatures at the interiorsurfaces of the chamber housing 102. This may promote thermaldissociation of gas molecules colliding with the interior surfaces ofthe chamber housing 102. In various embodiments, the thermal breaks 154,156 may be provided as voids or other thermally insulating barriersformed or disposed in the chamber housing 102 adjacent the ion sourcechamber 116.

As used herein, an element or operation recited in the singular andproceeded with the word “a” or “an” is to be understood as includingplural elements or operations, until such exclusion is explicitlyrecited. Furthermore, references to “one embodiment” of the presentdisclosure are not intended as limiting. Additional embodiments may alsoincorporate the recited features.

Furthermore, the terms “substantial” or “substantially,” as well as theterms “approximate” or “approximately,” can be used interchangeably insome embodiments, and can be described using any relative measuresacceptable by one of ordinary skill in the art. For example, these termscan serve as a comparison to a reference parameter, to indicate adeviation capable of providing the intended function. Althoughnon-limiting, the deviation from the reference parameter can be, forexample, in an amount of less than 1%, less than 3%, less than 5%, lessthan 10%, less than 15%, less than 20%, and so on.

Still furthermore, one of skill will understand when an element such asa layer, region, or substrate is referred to as being formed on,deposited on, or disposed “on,” “over” or “atop” another element, theelement can be directly on the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being“directly on,” “directly over” or “directly atop” another element, nointervening elements are present.

In view of the foregoing, at least the following advantages are achievedby the embodiments disclosed herein. A first advantage of the ion source100 described herein is the facilitation of larger beam currents ofatomic species, such as phosphorous, for a given extraction current,relative to ion sources having conventional cathode arrangements. Asecond advantage of the ion source 100 described herein is longermaintenance intervals. A third advantage of the ion source 100 describedherein is the provision of a smaller plasma volume since the plasma isgenerally confined within the tubular cathode 120 rather than fillingthe entire volume of the ion source chamber 116. A fourth advantage ismore efficient operation due to a shorter distance between the tubularcathode and the extraction aperture 110.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, the present disclosure has beendescribed herein in the context of a particular implementation in aparticular environment for a particular purpose. Those of ordinary skillin the art will recognize the usefulness is not limited thereto and thepresent disclosure may be beneficially implemented in any number ofenvironments for any number of purposes. Thus, the claims set forthbelow are to be construed in view of the full breadth and spirit of thepresent disclosure as described herein.

1. An ion source comprising: a chamber housing defining an ion sourcechamber and including an extraction plate on a front side thereof, theextraction plate having an extraction aperture formed therein; and atubular cathode disposed within the ion source chamber and having a slotformed in a front-facing semi-cylindrical portion thereof disposed in aconfronting relationship with the extraction aperture, wherein arear-facing semi-cylindrical portion of the tubular cathode directedaway from the extraction aperture is closed.
 2. The ion source of claim1, wherein the tubular cathode includes a main body having a first endcoupled to a cup containing a filament and a second end coupled to arepeller.
 3. The ion source of claim 2, wherein the cup extends througha sidewall of the chamber housing and is coupled to a cathode holder. 4.The ion source of claim 2, wherein the repeller includes a repeller headextending from a shaft, the shaft extending through a sidewall of thechamber housing and coupled to a repeller holder.
 5. The ion source ofclaim 1, wherein the extraction plate is formed of at least one ofsilicon, silicon carbide, aluminum, graphite, molybdenum, tantalum andtungsten.
 6. The ion source of claim 1, wherein the slot has an angularsize in a range of 10 degrees to 180 degrees relative to a circularcross-section of a main body of the tubular cathode.
 7. The ion sourceof claim 6, wherein the slot has an angular size of 60 degrees relativeto a circular cross-section of a main body of the tubular cathode. 8.The ion source of claim 6, wherein the slot has an angular size of 120degrees relative to a circular cross-section of a main body of thetubular cathode.
 9. The ion source of claim 6, wherein the slot has anangular size of 180 degrees relative to a circular cross-section of amain body of the tubular cathode.
 10. The ion source of claim 1, whereina radial distance between an exterior surface of a main body of thetubular cathode and an interior surface of the chamber housing is in arange of 1 millimeter to 5 millimeters.
 11. The ion source of claim 1,wherein a shortest distance between a main body of the tubular cathodeand the extraction aperture is in a range of 2 millimeters to 10millimeters.
 12. The ion source of claim 1, further comprising a thermalbreak in the chamber housing adjacent the ion source chamber formitigating temperature variations at an interior surface of the chamberhousing.
 13. The ion source of claim 12, wherein the thermal breakcomprises a void in the chamber housing.
 14. An ion source comprising: achamber housing defining an ion source chamber and including anextraction plate on a front side thereof, the extraction plate having anextraction aperture formed therein; and a tubular cathode disposedwithin the ion source chamber and having a slot formed in a front-facingsemi-cylindrical portion thereof disposed in a confronting relationshipwith the extraction aperture, wherein a rear-facing semi-cylindricalportion of the tubular cathode directed away from the extractionaperture is closed; wherein the slot has an angular size in a range of10 degrees to 180 degrees relative to a circular cross-section of a mainbody of the tubular cathode; wherein a radial distance between anexterior surface of the main body of the tubular cathode and an interiorsurface of the chamber housing is in a range of 1 millimeter to 5millimeters; and wherein a shortest distance between the main body ofthe tubular cathode and the extraction aperture is in a range of 2millimeters to 10 millimeters.
 15. A method of manufacturing an ionsource comprising: providing a chamber housing defining an ion sourcechamber and including an extraction plate on a front side thereof, theextraction plate having an extraction aperture formed therein; anddisposing a tubular cathode within the ion source chamber, the tubularcathode having a slot formed in a front-facing semi-cylindrical portionthereof, the slot disposed in a confronting relationship with theextraction aperture, wherein a rear-facing semi-cylindrical portion ofthe tubular cathode directed away from the extraction aperture isclosed.
 16. The method of claim 15, further comprising coupling a firstend of a main body of the tubular cathode to a cup containing a filamentand coupling a second end of the main body to a repeller.
 17. The methodof claim 15, wherein the slot has an angular size in a range of 10degrees to 180 degrees relative to a circular cross-section of a mainbody of the tubular cathode.
 18. The method of claim 15, wherein aradial distance between an exterior surface of a main body of thetubular cathode and an interior surface of the chamber housing is in arange of 1 millimeter to 5 millimeters.
 19. The method of claim 15,wherein a shortest distance between a main body of the tubular cathodeand the extraction aperture is in a range of 2 millimeters to 10millimeters.
 20. The method of claim 15, further comprising providing athermal break in the chamber housing adjacent the ion source chamber formitigating temperature variations at an interior surface of the chamberhousing.